A sustainable approach for the concurrent production of bioethanol and volatile compounds from agro residues using different yeast strains

This study explores the valorization of agricultural residues, specifically rice straw and mixed vegetables, for bioethanol and volatile compound production through optimized thermo-chemical pretreatment and fermentation. Acid and alkaline pretreatments were optimized using the Box–Behnken design (BBD), enhancing cellulose content by 1.5- and 1.9-fold in acid-pretreated rice straw and mixed vegetable wastes, respectively, while partially removing hemicellulose and lignin. FTIR analysis confirmed structural modifications and enzymatic hydrolysis improved sugar yields, with acid-pretreated mixed vegetables yielding 495.71 mg/g biomass. Fermentation with four yeast strains resulted in ethanol production, with KMnO₄-pretreated rice straw yielding 23.6 g/L ethanol with Pitchia kudriavzevii TISTR 5147 and mixed vegetables yielding 21.6 g/L ethanol with Saccharomyces cerevisiae TISTR 5606. Volatile compound profiling identified aroma-rich compounds such as phenyl ethanol and ethyl acetate, with Kluyveromyces marxianus TISTR 5616 producing the highest volatile abundance. Fermentation parameters, including temperature (30–36 °C), nitrogen content (5–15 g/L), and shaking speed (100–200 rpm), were optimized for improved volatile compound production. This study highlights the potential of agricultural waste for bioethanol and aroma compound production, presenting a sustainable biorefinery approach with industrial applications.